1. Field of the Invention
The present invention relates to hermetically sealed glass packages that are suitable to protect thin film devices that are sensitive to the ambient environment. Some examples of such devices are organic light emitting diode (OLED) displays, sensors, and other optical devices. The present invention is demonstrated using OLED displays as an example.
2. Description of Related Art
OLEDs have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). The traditional OLED displays are known as being very bright and having a good color contrast and wide viewing angle. However, the traditional OLED displays and in particular the electrodes and organic layers located therein are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. It is well known that the life of the OLED display can be significantly increased if the electrodes and organic layers within the OLED display are hermetically sealed from the ambient environment. Unfortunately, in the past it was very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that made it difficult to properly seal the OLED display are briefly mentioned below:                The hermetic seal should provide a barrier for oxygen (10-3 cc/m2/day) and water (10-6 g/m2/day);        The width of the hermetic seal should be small (e.g., <2 mm) so that it does not have an adverse effect on the size of the OLED display;        The temperature generated during a sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display. For instance, in a typical OLED display, the first pixels of OLEDs are located close to the hermetic seal and should not be heated to more than about 85-100° C. during the sealing process;        Any gases released during the sealing process should not contaminate the materials within the OLED display; and        The hermetic seal should enable electrical connections (e.g., thin-film electrodes) to enter the OLED display.        
Today the most common way for sealing the OLED display is to use different types of epoxies, inorganic materials and/or organic materials that form the seal after they are cured by ultra-violet light. Vitex Systems manufactures and sells a coating under the brand name of Barix™ which is a composite based approach where alternate layers of inorganic materials and organic materials can be used to seal the OLED display. Although these types of seals usually provide good mechanical strength, they can be very expensive and there are many instances in which they have failed to prevent the diffusion of oxygen and moisture into the OLED display. Another common way for sealing the OLED display is to utilize metal welding or soldering. However, the resulting seal is not durable in a wide range of temperatures because of the substantial differences between the coefficients of thermal expansions (CTEs) of the glass plates and metal in the OLED display.
The aforementioned problems and other shortcomings associated with traditional seals have been addressed in co-assigned U.S. Pat. No. 6,998,776 and published U.S. patent application No. 2005/001,545 (hereinafter the '776 patent and the '545 application) which are incorporated herein by reference. Briefly, the '776 patent and '545 application disclose that a hermetically sealed OLED display is manufactured by providing a first substrate plate and a second substrate plate, and depositing a frit onto the second substrate plate. OLEDs are deposited onto the first substrate plate. An irradiation source (e.g., laser, or infrared light) is then used to heat the frit, which forms a hermetic seal that connects the first substrate plate to the second substrate plate and also protects the OLEDs. The frit can be glass that is doped with at least one absorbing species, such as a transition metal, and optionally a CTE lowering filler, such that when the irradiation source heats the frit, it softens and forms a bond with the substrate plates, creating a hermetic seal. This type of frit can be softened and form the hermetic seal, while avoiding thermal damage to the OLEDs.
The frits disclosed in the '776 patent and '545 application, when pre-sintered as disclosed therein, form better seals if the pre-sintered frit is ground to reduce thickness variations. The need for grinding increases the cost and complexity of the OLED manufacturing process. Accordingly, it is desirable to obtain a chemically and mechanically stable, long lasting hermetic seal from pre-sintered frit without the need for a grinding step. Eliminating the grinding step reduces the cost and complexity of the OLED production process. This need and other needs are satisfied by the hermetic sealing technology of the present invention.